In mobile communication systems, frequency-division modulation (FDM) may be employed to share radio resources among multiple users. For example, radio resources are divided into multiple subcarriers in frequency domain and this divided resources are allocated to a plurality of users. In some cases, radio resources may also be divided in time domain to efficiently share among multiple users. Further, in such systems, when the users move relative to a radio base station, a frequency bandwidth of a subcarrier allocated to the user may be shifted up or down due to the Doppler effect. As a result, the reception of a signal transmitted through the subcarrier at the radio base station may interfere with the reception of another signal transmitted through an adjacent subcarrier.